This “people detector” with pyroelectric sensor was found in the April 1991 issue of Radio Electronics magazine. The circuit is based on an LM324 and a sensor from that time.
This source circuit was obtained in a 1976 publication for radio amateurs. The transistors can be...
This is the transmitter for the previous circuit. We found it in a 90s Electronics Now. The...
This circuit was found in a Popular Electronics from the 90s. The frequency is given by R2 and C1....